1. Field of Invention
The present invention relates generally to tissue stimulating prostheses, and in particular, to a controllable bypass pathway (or controllable shunt) for a tissue stimulating prosthesis.
2. Related Art
Certain medical devices, sometimes referred to as tissue-stimulating prostheses, operate by delivering an electrical stimulation to a recipient. These prostheses include, but are not limited to, pain relief stimulators, cardiac pacemakers, neural or neuromuscular stimulators, hearing prostheses, visual prostheses, etc. Hearing prostheses, such as a cochlear implants, brain stem implants, etc, deliver neural stimulation to a recipient's auditory system so as to evoke perception of a sound.
Neural stimulation conventionally delivers charge balanced stimuli. That is, the stimulation includes balanced negative and positive charges, so that no net positive or negative direct current (DC) is delivered to the recipient's tissue. This use of charge balanced stimuli prevents or reduces the production of harmful by-products at that interface that would occur through delivery of a DC current across the electrode/tissue interface.
Typically, a biphasic pulse pair is used to achieve charge balance. Such a stimulus is delivered as a positive charge pulse in phase 1, and an equal negative charge pulse in phase 2. The negative charge pulse typically has the same current and period as the positive pulse, but may alternatively be applied over a longer period or at lower amplitude. The important feature is that the total charge in phases 1 (positive) and 2 (negative) are equivalent.